Merge pull request #3324 from Soullivaneuh/travis-phpunit

PHPUnit / stable requirement

.travis.yml

@@ -51,7 +51,7 @@ before_script:
   - mkdir -p ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d && echo "memory_limit=-1" >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini
   - composer selfupdate
   - composer config -q -g github-oauth.github.com $GITHUB_OAUTH_TOKEN
-  - composer global require phpunit/phpunit:^4.8 fabpot/php-cs-fixer --no-update
+  - composer global require phpunit/phpunit:@stable fabpot/php-cs-fixer --no-update
   - composer global update --prefer-dist --no-interaction
   - if [ "$SYMFONY_VERSION" = "2.8.*@dev" ] || [ "$SYMFONY_VERSION" = "3.0.x-dev as 2.8" ]; then SYMFONY_DEPRECATIONS_HELPER=strict; fi;
   - if [ "$SYMFONY_VERSION" != "" ]; then composer require "symfony/symfony:${SYMFONY_VERSION}" --no-update; fi;